Multiple blade dampers for air exhaust ducts have been used in many locations where air is to be exhausted from an enclosure. Such a damper can be designed to control the volume of air flowing through the damper as required to control the condition in the enclosure or in the enhaust duct. Most such dampers, however, are able to control only major changes in the volume of air desired to be exhausted. Such dampers, therefore, are not capable of providing control both for major changes and for minor variations in the volume of air to be exhausted to accomplish close control of the condition under consideration.
Air exhaust ducts may be utilized for the discharge of air flowing through the ducts from many different sources, such as heat exchangers, combustion chambers, pressurized enclosures, mechanisms actuated by the flow of air which is finally discharged, etc. As a result it is desirable in many installations to be able to control the flow of air through the duct and thus to control the condition existing in the duct or in the apparatus from which the air flows through the duct.
It is, therefore, the principal object of the instant invention to provide a condition controlling air flow damper which can be adjusted to control major variations in the condition being controlled and also has means for "vernier-type" control of minor variations in the condition being controlled.
Because many of the conditions to be controlled by a damper embodying the invention result in the discharge through the damper of extremely high temperature air, it is yet another important object of the instant invention to provide for contraction and expansion of the elements of the damper, as their temperatures change, in such fashion that the damper functions properly at either extreme of the temperature to which it is subjected during normal operation, during what might be called "stand-by" operation and during transition from one to the other.
A more specific object of the instant invention is to provide an air flow control damper responsive to major changes and with vernier-like movements to provide for control of the temperature of a liquid heat-exchange medium which is subject to solidification if cooled too greatly and which normally operates at extremely high temperature, for example, liquid sodium, utilized as a heat exchange medium in an atomic energy generating plant.